The present invention relates to an enhanced multi-user receiving apparatus for a code division multiple access (CDMA) system; and, more particularly, to an integrated receiving apparatus of a subtractive interference cancellation receiver and an adaptive minimum mean squared error (MMSE) receiver for a CDMA system.
In general, techniques about adaptive MMSE receivers are disclosed in articles, such as S. L. Miller and A. N. Barbosa, xe2x80x9cA Modified MMSE Receiver for Detection of DS-CDMA Signals in Fading Channelsxe2x80x9d, Proc. MILCOM""96, pp. 898-902 and M. Latvaaho and M. Juntti, xe2x80x9cModified Adaptive LMMSE Receiver for DS-CDMA Systems in Fading Channelsxe2x80x9d, Proc. PIMRC""97, pp. 554-558.
An adaptive MMSE receiver shows much better performance than a conventional CDMA receiver does in a static channel. Also, the adaptive MMSE receiver can suppress out-of-cell interference in a multi-cell channel environment. However, the radio channels are not static but time varying and fading. In fading environments, specifically under the low signal to interference plus noise ratio (SINR) during the deep fading, the performance of the adaptive MMSE receiver is severely degraded.
And, a thesis, M. K. Varanasi and B. Aazhang, xe2x80x9cMultistage detection in asynchronous code-division multiple-access communications xe2x80x9cIEEETr. on Commun., vol. 38, No. 4, pp. 509-519, April 1990 and another thesis S. R. Kim, J. G. Lee and H. Lee, xe2x80x9cInterference cancellation scheme with simple structure and better performancexe2x80x9d Electronic Letters, November 1996, vol. 32, No. 23, pp. 2115-2117 refer to an apparatus of a subtractive interference cancellation receiver.
The subtractive interference cancellation receiver has better performance in comparison with an existing conventional CDMA receiver in a general wireless channel environment. However, the subtractive interference cancellation receiver cannot suppress the interference caused by other cells in multiple cell environments.
It is, accordingly, an object of the present invention to provide an integrated receiving apparatus of a subtractive interference cancellation receiver and an adaptive MMSE receiver that is capable of overcoming limitations of the subtractive interference cancellation receiver and the adaptive MMSE receiver and having improved performance.
In accordance with one aspect of the present invention, there is provided an apparatus for canceling an interference signal by using a parallel multi-stage structure in a code division multiple access (CDMA) system, comprising: a delay unit for delaying the receiving signal in regular sequence; and an interference cancellation unit for canceling the interference of the signal, which is delayed and transmitted through said delay unit.
In accordance with another aspect of the present invention, there is provided a method for canceling an interference signal by using a parallel multi-stage structure in a code division multiple access (CDMA) system, comprising the steps of: a) delaying a receiving signal; b) receiving and predicting data and channel parameter from the individual user; c) regenerating the interference signal of the individual user by using the data and the channel parameter predicted by the multiple receiving and predicting; and d) canceling all the interference signals delayed and transferred through the delaying by the interference signal regenerated through the multiple interference regeneration.